Method and device for determining input voltage of inverter circuit and magnetic resonance imaging system

Abstract

Methods, devices, and apparatus for determining an input voltage of an inverter circuit in a magnetic resonance imaging system are provided. In one aspect, a method includes: determining a maximum inductance voltage value corresponding to a maximum current value of a current sequence according to a relationship between inductance voltage and inductance current of a gradient coil, determining a minimum DC voltage value corresponding to the maximum inductance voltage value according to a relationship between output voltage and input voltage of the inverter circuit, and controlling the input voltage into an input terminal of the inverter circuit to have the minimum DC voltage value when the current sequence is input into a control terminal of the inverter circuit. The inverter circuit is configured to generate an AC voltage based on the input voltage and the current sequence and output the AC voltage to the gradient coil.

What is claimed is: 
     
       1. A method of determining an input voltage of an inverter circuit of a magnetic resonance imaging system, the method comprising:
 determining a maximum inductance voltage value corresponding to a maximum current value of a current sequence by calculating an inductance voltage of a gradient coil of the magnetic resonance imaging system according to a relationship between inductance voltage and inductance current of the gradient coil of the magnetic resonance imaging system; 
 determining a minimum DC voltage value corresponding to the maximum inductance voltage value by calculating an input voltage of the inverter circuit according to a relationship between the inductance voltage of the gradient coil and input voltage of the inverter circuit; and 
 controlling the input voltage into an input terminal of the inverter circuit to have the minimum DC voltage value when the current sequence is input into a control terminal of the inverter circuit, 
 wherein the inverter circuit is configured to generate an AC voltage based on the input voltage and the current sequence and output the generated AC voltage to the gradient coil via an output terminal of the inverter circuit. 
 
     
     
       2. The method of  claim 1 , wherein the input voltage of the inverter circuit is provided by a controllable DC power supply. 
     
     
       3. The method of  claim 2 , wherein the controllable DC power supply comprises a silicon control rectifier (SCR) circuit. 
     
     
       4. The method of  claim 2 , wherein the controllable DC power supply is configured to output a DC voltage through a closed-loop control with the minimum DC voltage value as a reference value and an actual value of the DC voltage into the inverter circuit as a feedback value. 
     
     
       5. The method of  claim 4 , wherein the inverter circuit comprises a plurality of cascaded H-bridges, and a voltage acquisition sensor is disposed at the output terminal of the inverter circuit and configured to obtain a pulsed voltage at the output terminal of the inverter circuit,
 wherein the method further comprises:
 sampling the pulsed voltage to obtain a sampled voltage; and 
 determining the actual value of the DC voltage input into each of the H-bridges from the sampled voltage according to different phases for the H-bridges. 
 
 
     
     
       6. The method of  claim 4 , further comprising:
 comparing the minimum DC voltage value with the actual value of the DC voltage to obtain a comparison result; 
 processing the comparison result by a proportional-integral-derivative (PID) controller to obtain a processed result; and 
 adjusting a conduction angle of the controllable DC power supply by pulse width modulation (PWM) based on the processed result such that the actual value of the DC voltage is substantially identical to the minimum DC voltage value. 
 
     
     
       7. The method of  claim 1 , wherein the relationship between inductance voltage and inductance current of the gradient coil is expressed as below: 
       
         
           
             
               
                 Vgc 
                 = 
                 
                   
                     Lgc 
                     × 
                     
                       
                         d 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         Igc 
                       
                       dt 
                     
                   
                   + 
                   
                     Igc 
                     × 
                     Rgc 
                   
                 
               
               , 
             
           
         
         where Vgc represents the inductance voltage, Lgc represents an inductance of the gradient coil, Igc represents the inductance current, Rgc represents an equivalent resistance of the gradient coil, and t represents time. 
       
     
     
       8. The method of  claim 1 , wherein the relationship between the inductance voltage of the gradient coil and input voltage of the inverter circuit is expressed as below:
     Vgc=nV out=(2 D −1)× nV bus,
 
 where Vgc represents an inductance voltage of the gradient coil, Vbus and Vout respectively represent an input voltage of an H-bridge of the inverter circuit, n represents a number of H-bridges of the inverter circuit, and D represents the duty cycle. 
 
     
     
       9. A device for determining an input voltage of an inverter circuit of a magnetic resonance imaging system, the device comprising:
 at least one processor; 
 at least one non-transitory machine-readable storage medium coupled to the at least one processor having machine-executable instructions stored thereon that, when executed by the at least one processor, cause the at least one processor to perform operations comprising:
 determining a maximum inductance voltage value corresponding to a maximum current value of a current sequence by calculating an inductance voltage of a gradient coil of the magnetic resonance imaging system according to a relationship between inductance voltage and inductance current of the gradient coil of the magnetic resonance imaging system; and 
 determining a minimum DC voltage value corresponding to the maximum inductance voltage value by calculating an input voltage of the inverter circuit according to a relationship between the inductance voltage of the gradient coil and input voltage of the inverter circuit; and 
 
 a controller configured to control the input voltage into an input terminal of the inverter circuit to have the minimum DC voltage value when the current sequence is input into a control terminal of the inverter circuit, 
 wherein the inverter circuit is configured to generate an AC voltage based on the input voltage and the current sequence and output the generated AC voltage to the gradient coil via an output terminal of the inverter circuit. 
 
     
     
       10. The device of  claim 9 , wherein the input voltage of the inverter circuit is provided by a controllable DC power supply. 
     
     
       11. The device of  claim 10 , wherein the controllable DC power supply comprises an SCR circuit. 
     
     
       12. The device of  claim 10 , wherein the controller is configured to:
 perform a closed-loop control on a DC voltage output from the controllable DC power supply by taking the minimum DC voltage value as a reference value and an actual value of the DC voltage into the inverter circuit as a feedback value. 
 
     
     
       13. The device of  claim 12 , wherein the inverter circuit comprises a plurality of cascaded H-bridges, and
 wherein the controller is configured to:
 obtain a pulsed voltage at the output terminal of the inverter circuit from a voltage acquisition sensor disposed at the output terminal of the inverter circuit; 
 obtain a sampled voltage by sampling the pulsed voltage; and 
 determine the actual value of the DC voltage input into each of the H-bridges from the sampled voltage according to different phases for the H-bridges. 
 
 
     
     
       14. The device of  claim 12 , wherein the controller comprises:
 a comparator configured to compare the minimum DC voltage value with the actual value of the DC voltage to obtain a comparison result; 
 a proportional-integral-derivative (PID) controller configured to process the comparison result to obtain a processed result; and 
 a pulse width modulator configured to adjust a conduction angle of the controllable DC power supply based on the processed result such that the actual value of the DC voltage is substantially identical to the minimum DC voltage value. 
 
     
     
       15. A magnetic resonance imaging system comprising:
 a gradient power amplifier comprising:
 a DC power supply configured to output a DC voltage; 
 an inverter circuit connected to the DC power supply at an input terminal and configured to generate an AC voltage according to the DC voltage and a current sequence; 
 
 a spectrum analyzer connected to a control terminal of the inverter circuit and configured to output the current sequence to the inverter circuit; 
 a gradient coil connected to an output terminal of the inverter circuit and configured to receive the AC voltage from the inverter circuit; and 
 a device for determining an input voltage of the inverter circuit, the device comprising:
 at least one processor; 
 at least one non-transitory machine-readable storage medium coupled to the at least one processor having machine-executable instructions stored thereon that, when executed by the at least one processor, cause the at least one processor to perform operations comprising:
 determining a maximum inductance voltage value corresponding to a maximum current value of the current sequence by calculating an inductance voltage of the gradient coil according to a relationship between inductance voltage and inductance current of the gradient coil; and 
 determining a minimum DC voltage value corresponding to the maximum inductance voltage value by calculating an input voltage of the inverter circuit according to a relationship between the inductance voltage of the gradient coil and input voltage of the inverter circuit; and 
 
 a controller configured to control the input voltage into the input terminal of the inverter circuit to have the minimum DC voltage value when the current sequence is input into the control terminal of the inverter circuit. 
 
 
     
     
       16. The magnetic resonance imaging system of  claim 15 , wherein the DC power supply is a controllable DC power supply, and
 wherein the controller is configured to perform a closed-loop control on a DC voltage output from the controllable DC power supply by taking the minimum DC voltage value as a reference value and an actual value of the DC voltage into the inverter circuit as a feedback value. 
 
     
     
       17. The magnetic resonance imaging system of  claim 16 , wherein the inverter circuit comprises a plurality of cascaded H-bridges, and
 wherein the controller comprises:
 a voltage acquisition sensor disposed at the output terminal of the inverter circuit and configured to obtain a pulsed voltage at the output terminal of the inverter circuit; and 
 a sampling circuit configured to sample the pulsed voltage to obtain a sampled voltage, and 
 
 wherein the controller is configured to determine the actual value of the DC voltage input into each of the H-bridges from the sampled voltage according to different phases for the H-bridges. 
 
     
     
       18. The magnetic resonance imaging system of  claim 16 , wherein the controller comprises:
 a comparator configured to compare the minimum DC voltage value with the actual value of the DC voltage to obtain a comparison result; 
 a proportional-integral-derivative (PID) controller configured to process the comparison result to obtain a processed result; and 
 a pulse width modulator configured to adjust a conduction angle of the controllable DC power supply based on the processed result such that the actual value of the DC voltage is substantially identical to the minimum DC voltage value. 
 
     
     
       19. The magnetic resonance imaging system of  claim 15 , wherein the spectrum analyzer is configured to output the current sequence to the inverter circuit after the input voltage of the inverter circuit is adjusted to have the minimum DC voltage value. 
     
     
       20. The magnetic resonance imaging system of  claim 19 , wherein the spectrum analyzer is configured to calculate a respective current sequence corresponding to an imaging sequence for each imaging scan, and
 wherein the input voltage of the inverter circuit is adjusted to have the minimum DC voltage value between an interval of two adjacent imaging scans.